Sickle cell disease (SCD) is a poorly treated debilitating condition for which we are developing a promising, new oral prophylactic therapy. A dire need exists for our drug, as millions of patients who have inherited SCD world-wide, ~100,000 in the US, continue to suffer with episodic pain, disability, and premature death. Hydroxyurea treatment has clear-cut deficiencies, and many drugs under development target treatment rather than prevention of acute events. The cause of most SCD morbidity is abnormal blood flow, notably acute pain crises that result from stoppage of microvascular flow. Defective blood flow results from multiple pathophysiologies, includin several that are independent of the paradigmatic sequence of deoxygenation -> sickle hemoglobin polymerization -> red cell sickling. Based on evidence that endothelial P-selectin is central to ongoing impairment and acute stoppage of flow, we are targeting this adhesion molecule with our therapy. In vitro and preliminary clinical data show that pentosan polysulfate sodium (PPS) improves microvascular blood flow in SCD. However, commercially available PPS is not ideal therapy because of its marginal oral bioavailability and limited duration of action. Accordingly, we have devised two synergetic plans to develop improved second generation PPS-2 that will provide increased oral bioavailability so all patients will receive therapeutic amounts of PPS and prolonged absorption so that the frequency of PPS administration will be reduced and patient compliance enhanced. One plan employs direct formulation of parent PPS; the other employs fractionation of PPS, identification of pharmaceutically superior PPS fractions, and formulation of the optimal fraction. This proposal focuses on the fractionation strategy. Lower molecular weight PPS fractions have better oral bioavailability and less anticoagulant activity than unfractionated PPS. We first will test PPS fractions of different molecular weighs to identify the two lowest molecular weight fractions that have robust P-selectin blocking activity and safe anticoagulant activity. Then we will test those two for oral bioavailability and pharmacokinetics in monkeys, the best nonhuman model of human bioavailability and pharmacokinetics. These studies will use high doses of radiolabeled PPS compounds to obtain the best bioavailability/pharmacokinetic data for PPS to date and first such dat for PPS fractions. These studies will identify the most favorable PPS fraction to be formulated and developed as PPS-2 and will enable filing a composition of matter patent. Our overarching goal is to improve the quality of life of SCD patients by bringing to market an effective oral P-selectin blocking drug for long-term administration to prevent sickle red blood cell sticking to the lining of blood vessels, improve blood flw, and avert acute painful episodes. This Phase I SBIR will provide a superior PPS fraction for PPS-2 formulation and development. Subsequent fractionation, formulation, preclinical testing in vitro and in sickle cell mice, GMP production, and IND filing ill be achieved with support of a Phase II SBIR grant.